ATCC BACTeriAl CulTure Guide - ATCC: The Global Bioresource Center
Bacteria Growth in the laboratory (in vitro). Bacterial nutrition and the design of culture media...
Transcript of Bacteria Growth in the laboratory (in vitro). Bacterial nutrition and the design of culture media...
Bacterial nutrition and the design of culture media
• Based on bacterial metabolism*
• Culture pH
• Culture oxidation- reduction petencial
• Gaseous requirments– Oxzgen
Oxygen concentration
• Aerobs
• Anaerobs (do not require oxygen)
• Obligate anaerobs (die in the presence of O)
• Facultative anaerobs (E.coli)
• Microaerophilic bacteria
Temperature ( characteristic ranges)
• Psychrophiles: with optimum growth T around 20 C
• Mesopihles: between 15 and 45 with optimum around 37 C
• Thermophiles: between 30 and 75 with optimum around 55 C
• Hyperthermophiles: T grater than 100C
Techniques used to study bacteria
• Aseptic (sterile) techniques:
• Sterile media
• To prevent contamination (accidental intorduction of unknown bacteria)
• Sterilisation (autoclave, flaming)
• Desinfection (the removal of potentially harmful microbes : B, V,
Baceria are grown (cultured)
• Growth media:• Liquid (for large
numbers of bcteria)• Solid (for isolation of
individual bacteria)• Semisolid ( for
demonstration of motility)
• Envinronmental conditions:
optimal temperature, oxygen concentration, pH,
water activity
Growth media
• Defined media (synthetic)- composed form defined ingredients
• Complex media – composed from undefined ingredients such as proteolytic digests of meat (peptons) and meat extracts– Nutrient broth, tryptic soya broth– Nutrient agar,…– Blood- an addtive to media
Obtaining bacterial colonies
• Pure culture
• Isolation – using method called streaking
• To strake bacteria on to agar plates we are using a wire (or plastic) loop
Selective and differential media
• Selective media: for selection of particular groups of bacterial pathogens ( contain inhibitors i.e. antibiotics, bile salts, dyes, which are suppressing the growth of unwonted bacteria)
• Differential media: for differentiation of two species or groups (lactose +, -)
Agar isolated from seaweed
• Is not degradated by bacteria
• Agar is melted by boiling
• Liquid medium can be converted into solid medium by the adition of agar (1- 2%) or semisolid medium (0,6%)